The present invention relates to a water current energy converter designed for and capable of converting the flow energy of a moving body of water into electric power, such converter comprising at least one water driven flow machine, especially a water turbine, an electric power generator, and a hydraulic energy transfer system arranged between said water turbine(s) and said power generator.
The known types of contemporary hydroelectric machines for generating electric power by making use of the flow energy of moving bodies of water embody the different types of water driven turbines that have been developed to highly sophisticated technical standard. With hitherto known such machines, maintaining a constant speed of revolution of the water driven turbines used for power generation is a primary requirement. The maintenance of constant speed can be effected by continuously adjusting, during operation, either the blade angle of the turbine propeller blades, or the wheel discharge of the turbine, the latter usually performed by turbine gate rigging, i.e. by continuously altering the position of baffle plates arranged within the inlet area of the turbine wheel passage. Both ways of speed control mentioned require elaborate and thus, expensive machinery with inherent tendency to operation failures, and also with losses of efficiency involved.
Another technical problem lies in the fact that an A.C. voltage of the frequency range between 50 to 54 Hz usually required for industrial purposes can only be generated by water driven turbines of a rated speed of 100 to 600 revolutions per minute if an electric power generator of considerable size, i.e. diameter, is coupled to the turbine shaft. Alternatively, a generator of reduced diameter should be driven by the water turbine via a speed reducing gear whereby mechanical efficiency is reduced by simultaneous increase of investment and maintenance expenditures. For the sake of example only, reference is made to an existing power plant situated at the mouth of the river Ronce in France where an electric power generator of the diameter of 4 meters is driven by an adjustable blade Kaplan-type turbine having an impeller of the diameter of 5.35 meters and operating at a rated speed of 93.75 revolutions per minute. Such and similar large size equipment can economically be used in connection with huge dams or weirs only. Such types of machinery are, however, completely excluded from possible use in all cases where the utilization of the energy of water flow, especially tidal currents of only 1 to 2 or even 4 to 5 meters in thickness of layer, and of up to 40 km per hour speed of advance is envisaged.
Water currents of such characteristics are occasionally several thousand meters wide and their estimated total energy content could be a multiple of that of the famous Niagara Falls. According to both, local observations and measured values, on the river Amasonas heavy break-ins of tidal current in the form of an advancing wall-like tidal surge speeding up to 40 km per hour against the river stream and having a height of 4.5 meters by a width of 12 km are quite common at times of sun-moon conjunction. Sources of literature refer to tidal surges observed at the mouth of the river Humber that occure twice a day with a flow speed up to 40 km per hour. In a distance of 10 km further upstream from the mouth, the height of the tidal wave could still be estimated to 2 meters. Similarly to this, the speed of the tidal current through the mouth of the river Seine has also been measured to 40 km per hour, and its height can also reach 2 meters. In certain areas between sea islands and in narrows tidal currents of higher speed than those mentioned above involving extremely huge masses of water have also been located. It is a well known experience to those familiar with navigation that in certain periods of flood tide, cargo vessels of minor or even average performance have their difficulty of passing the Straits of Gibraltar.